https://www.gamespot.com/articles/destiny-2-servers-going-offline-tomorrow/1100-6455571/

Destiny 2's servers will be offline tomorrow, December 12, as developer Bungie rolls out the 1.1.1.1 update for everyone on PS4, Xbox One, and PC to install. In a blog post, Bungie confirmed that the server maintenance will begin at 7 AM PT tomorrow, and at this time, you won't be able to log in to the game. At 8 AM PT, everyone who is in an activity will be kicked to the main screen as the maintenance is conducted.

The maintenance is expected to run for a period of six hours, wrapping up at 2 PM PT. You can see a timeline for the Destiny 2 scheduled maintenance in the chart below.